1. Field of the Invention
The present invention relates to an apparatus for forming an image and a method therefor, and more particularly, to a developing apparatus adapted for use in an image forming apparatus using electrophotography, and a method of forming an image using the developing apparatus.
2. Description of the Related Art
In an image forming apparatus using electrophotography, a photosensitive object is exposed to light, and then, a latent electrostatic image invisible to the naked eye is formed on a portion of the photosensitive object according to image information obtained from an original copy or a predetermined source. Next, a developing solution (toner) is applied onto the portion of the photosensitive object to visualize the latent electrostatic image. Then, the visualized image is transferred to and fixed onto paper.
The image forming apparatus using electrophotography is classified into a wet-type image forming apparatus and a dry-type image forming apparatus according to the type of toner used. The wet-type image forming apparatus uses a mixture of powdered toner and a volatile liquid carrier as a developing solution, whereas the dry-type image forming apparatus uses only powdered toner.
In the image forming apparatus using electrophotography, the developing solution is supplied to the photosensitive object to visualize the latent electrostatic image formed thereon. Specifically, FIGS. 1 and 2 are cross-sectional views of conventional developing apparatuses in the dry-type image forming apparatus using electrophotography.
Referring to FIG. 1, a charging roller 12 charges the circumference of a photosensitive drum 10 with an electric charge. When a laser beam containing image information is scanned on a portion of the charged circumference of the photosensitive drum 10 by a laser scanning unit 14, a static electric charge of the portion is removed, and then, a latent electrostatic image corresponding to the image information is formed on the circumference of the photosensitive drum 10. The latent-electrostatic image can be visualized by a developing roller 16 supplying toner charged with the same or opposite electric charge to the circumference of the photosensitive drum 10. The developing roller 16 is supplied with toner by a supply roller 20. A portion of the supply roller 20 is in contact with the circumference of the developing roller 16, and another portion of the supply roller 20 is in contact with toner 18.
Above the developing roller 16, a toner layer control unit 22 is installed adjacent to the circumference of the developing roller 16 so as to control a toner layer formed on the circumference of the developing roller 16. Also, below the developing roller 16, first and second seal members 24 and 28 are installed to seal a first case 20 containing the toner 18 and the supply roller 20, and a bottom of the first case 26 is connected to the toner layer control unit 22. In an opposite side of the developing roller 16, a waste toner storage member 32, which stores waste toner collected from the circumference of the photosensitive drum 10 after the latent electrostatic image has been transferred onto paper (not shown), is disposed in a second case 34 having the charging roller 12.
Also, to prevent the leakage of the waste toner, a third seal member 30 is connected to a bottom of the second case 34 while being in contact with the circumference of the photosensitive drum 10. A cleaning blade 36, which is used to remove the waste toner remaining on the circumference of the photosensitive drum 10, is installed adjacent to the charging roller 12 in the waste toner storage member 32 and between the charging roller 12 and the third seal member 30. Here, reference numeral 38 denotes a lid of a toner storage member 40 of the first case 26.
FIG. 2 is a cross-sectional view of another conventional developing apparatus in an image forming apparatus. Referring to FIG. 2, a charging apparatus 52, which has the same operations as the charging roller 12 of FIG. 1, is installed adjacent to a photosensitive drum 50. In the front of the charging apparatus 52 is installed a discharging lamp 54 removing an electric charge from the circumference of the photosensitive drum 50 prior to charging the photosensitive drum 50. When an exposure apparatus 21 emits light on the circumference of the photosensitive drum 50 charged by the charging apparatus 52, a latent electrostatic image is formed on the circumference of the photosensitive drum 50. The formed latent electrostatic image can be visualized by a developing apparatus 56 installed adjacent to the photosensitive drum 50.
A toner hopper 60 containing toner 58 is installed in an upper portion of a case 56a. A developing roller 62, which supplies the toner 58 to the photosensitive drum 50 so as to visualize the latent electrostatic image, is installed at an aperture at a lower portion of the case 56a. Between the developing roller 62 and a toner outlet of the toner hopper 60 is installed a supply roller 64 supplying the toner 58 to the developing roller 62. An upper side of the circumference of the developing roller 62 is in contact with a toner layer control unit 66 controlling an amount of the toner 58 and toner layers formed on the developing roller 62, and a lower side of the developing roller 62 is in contact with a sealing blade 68 preventing the leakage of the toner 58 out of the case 56a. 
A cleaning roller 70 is installed at an upper aperture of the case 56a and is separated from a lower aperture of the case 56a by a predetermined distance. The cleaning roller 70 is spaced-apart from the photosensitive drum 50 by about 200 xcexcm and is used to remove the toner 58 remaining on the circumference of the photosensitive drum 50. The upper and lower sides of the circumference of the cleaning roller 70 are in contact with a toner layer control unit 66, which controls the amount of the toner 58 and the toner layers, and a sealing blade 74, which prevents the leakage of the toner 58, respectively. The developing roller 62 and the cleaning roller 70 are connected to a power source 76 supplying a predetermined cleaning and developing voltage thereto so as to remove the toner 58 remaining on the circumference of the photosensitive drum 50, supply the toner 58 to the circumference of the photosensitive drum 50, and visualize the latent electrostatic image formed on the circumference of the photosensitive drum 50.
The conventional developing apparatus of FIG. 1 may perform an excellent cleaning operation since the toner remaining on the circumference of a photosensitive drum is mechanically removed by a blade when a latent electrostatic image is transferred on paper and then cleaned. However, the conventional developing apparatus of FIG. 1 is disadvantageous in that it is difficult to minimize the conventional developing apparatus in size since a region for additionally storing waste toner is required, there is a limitation in reducing at toner consumption due to the waste toner, and additional devices are further needed to collect and store the waste toner when the image forming apparatus is manufactured. These disadvantages would cause an inconvenience of a user and contamination of an image.
On the other hand, the conventional developing apparatus of FIG. 2 may perform less excellent cleaning operations than that of the developing apparatus of FIG. 1, but is advantageous in that it does not require an additional space for storing the waste toner. However, the developing apparatus of FIG. 2 has a low efficiency in collecting the waste toner from a photosensitive drum, thereby still causing the contamination of an image, such as a ghost image, due to a poor cleaning operation.
To solve the above and other problems, it is an object of the present invention to provide a developing apparatus adapted for use in an image forming apparatus that does not need any additional cleaning device and a waste toner storage space, thereby reducing the image forming apparatus in size and consumption of toner by a significant amount, and that is durable to generate an image of good quality since the contamination of an image generated due to the poor cleaning operation is prevented.
It is another object of the present invention to provide a method of forming an image using a developing apparatus in an image forming apparatus.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects, there is provided a developing apparatus adapted for use in an image forming apparatus capable of visualizing a latent electrostatic image formed on a circumference of a photosensitive drum. The developing apparatus includes a retrieving/auxiliary developing roller being in contact with the circumference of the photosensitive drum to retrieve and collect toner remaining around a region of the circumference of the photosensitive drum and to first develop the latent electrostatic image, a first toner layer control member uniformly re-distributing the retrieved (remnant) toner and regulating the electrification of the remnant toner on the circumference of the retrieving/auxiliary developing roller, a developing roller having a gap with the circumference of the photosensitive drum and secondly developing the firstly developed latent electrostatic image so as to completely visualize the latent electrostatic image, a supply roller supplying new toner to the developing roller, and a second toner layer control member regularly and uniformly coating the new toner, which is supplied by the supply roller, throughout the circumference of the developing roller and regulating the amount of the electrification of the new toner of the developing roller.
The developing apparatus includes a first seal member sealing the retrieving/auxiliary developing roller, and toner supplying elements formed between the developing roller and the retrieving/auxiliary developing roller, and a second seal member sealing the developing roller, and the case containing the toner supplying elements.
The developing apparatus includes a power source supplying a predetermined voltage to the retrieving/auxiliary developing roller so as to retrieve (collect) the toner remaining on peripheral regions other than an latent electronstatic image region of the circumference of the photosensitive drum, and to firstly develop the latent electrostatic image.
The developing apparatus includes another power source supplying the developing roller with a developing voltage having an absolute value being greater than that of the latent electrostatic image. The developing apparatus includes another power source supplying the first toner layer control member with a first control voltage having an absolute value or greater than that of the predetermined voltage supplied to the retrieving/anxiliary developing roller.
The developing apparatus includes another power source supplying the supply roller and the second toner layer control member with a supplying voltage and a second control voltage each having an absolute value being equal to or greater than the absolute value of the voltage supplied to the developing roller.
The developing apparatus includes another power source connected to the supply roller and the second toner layer control member to supply a developing voltage to the developing roller so that the absolute value of an electric potential of the circumference of the developing roller is greater than the absolute value of an electric potential of the latent electrostatic image, and to supply the supply roller and the second toner layer control member with the supplying voltage and the second voltage, respectively, each having an absolute value being equal to or greater than that of the developing voltage supplied to the developing roller.
An electric potential VB1 of the circumference of the retrieving/auxiliary developing roller has a relationship with an electric potential VL of the latent electrostatic image formed on the circumference of the photosensitive drum and an electric potential V0 around the latent electrostatic image as follows:
|VL| less than |VB1| less than |V0|]
The power source supplying the developing voltage to the developing roller includes DC and AC power sources.
The power source, which is connected to the developing roller, the supply roller and the second toner layer control member, includes the AC power source, a first DC power source, and a second DC power source. The power source supplies the developing voltage made by overlapping DC and AC voltages of the AC power source and the second DC power source, respectively, to the developing roller. The first DC power source and the second DC power source supplies the developing roller and the second toner layer control member with a developing voltage and a second control voltage, respectively, each having a DC voltage having absolute value being equal to greater than the absolute value of a DC voltage applied to the developing roller.
To achieve the above and other objects, there is provided a method of forming an image using a developing apparatus in an image forming apparatus. The method includes primarily developing a latent electrostatic image with the retrieved toner while retrieving (collecting) toner remaining around the latent electrostatic image formed on the circumference of a photosensitive drum, secondly developing and completely visualizing the latent electrostatic image with new toner while keeping a predetermined gap between the developing roller and the circumference of the photosensitive drum, and supplying the new toner to the developing roller. In the method, the circumference of the photosensitive drum is charged with a first electric potential in response to an image forming initial signal, a predetermined region of the circumference of the photosensitive surface, which is charged with the first electric potential, is exposed to light to have a second electric potential, and the circumference of the retrieving/auxiliary developing roller is charged with a third electric potential, wherein the first, second, and third electric potentials have the following relationship:
|second electric potential| less than |third electric potential| less than |first electric potential|
The retrieving/auxiliary developing roller is set to have a predetermined linear velocity with respect to the circumference of the photosensitive drum. The first control voltage supplied to the first toner layer control member has a larger absolute value than the predetermined voltage supplied to the retrieving/auxiliary developing roller so as to keep or enhance friction electrification characteristics of toner.
The developing voltage supplied to the developing roller has an absolute value of the electric potential of the circumference of the developing roller greater than that of the predetermined voltage of the circumference of the retrieving/auxiliary developing rollers, and the supplying voltage and the second control voltage, which are equal to or greater than the developing voltage applied to the developing roller, are supplied to the supply roller and the second toner layer control member, respectively.
To achieve the above and other objects, there is provided a method of forming an image in a developing apparatus of in an image forming apparatus. The method includes charging the circumference of the photosensitive drum with a first electric potential in response to an image forming initial signal, forming a latent electrostatic image of a second electric potential on the circumference of the photosensitive drum, which has been charged with the first electric potential, partially visualizing the latent electrostatic image, completely visualizing the partially visualized latent electrostatic image, and transferring and fixing the completely visualized latent electrostatic image onto paper.
The completely visualizing of the partially visualized latent electrostatic image includes firstly developing the latent electrostatic image while retrieving (collecting) remnant toner from a non-image region other than an image region of the circumference of the photosensitive drum, which has been charged with the first electric potential.
The retrieving of the remnant toner and firstly developing the latent electrostatic image are performed using the retrieving/auxiliary developing roller whose circumference has been charged with a third electric potential and that satisfies the following:
|second electric potential| less than |third electric potential| less than |first electric potential|
The completely visualizing of the partially visualized latent electrostatic image includes secondly developing the firstly developed latent electrostatic image using the developing roller charged with the developing voltage generated by overlapping a DC voltage and an AC voltage.
As described above, in a developing apparatus of an image forming apparatus according to embodiments of the present invention, the remnant toner remaining along the circumference of a photosensitive drum is retrieved to be used in developing a latent electrostatic image. Thus, since no additional cleaning devices are required and no waste toner is generated, the developing apparatus does not require an additional space for storing the waste toner, thereby reducing the developing apparatus in size. Also, since the remnant toner is used again, the consumption of toner decreases. Further, a retrieving ratio of the remnant toner can be increased by controlling a retrieving/auxiliary developing roller to be in contact with a photosensitive drum, and an image of high definition can be formed while the retrieving/auxiliary developing roller is not in contact with a developing roller. Because there is no need of an additional space for storing the waste toner, it is possible to prevent any inconvenience of a user and the contamination of an image or the pollution of environments due to the leakage of the waste toner. Lastly, the developing apparatus is improved in structure and functions so that the life of the developing apparatus can be lengthened.